During the past year, our research has continued its investigation of central nervous system (CNS) serotonin correlates of low CSF 5-HIAA and tolerance to the intoxicating effects of alcohol. To assess the role of impaired serotonin functioning and intrinsic tolerance on excessive alcohol consumption, CSF was obtained from alcohol naive rhesus macaques. Subjects were then dispensed identical doses of IV alcohol and rated by experienced observers for levels of intoxication. (1) To validate our ratings, a new methodology was used to assess the degree of intoxication that each subject exhibited after identical alcohol dosages. Subjects with low ratings for intoxication and low CSF 5-HIAA took longer to escape from a two meter high Plexiglass chamber. They were also more likely to fall and bump against the wall. (2) As had been shown in our previous studies, peer-reared monkeys (monkeys reared without adults, with only age-mates present), exhibited lower CSF 5-HIAA concentrations and were rated as less intoxicated than mother reared subjects. They were also more likely to consume alcohol to excess. Peer-reared monkeys were also more likely to receive aggression from their agemates, and to exhibit fear-related behavior. (3) A collaboration was initiated with Dr. Stanley Watson, at the University of Michigan, to quantify neuroanatomical differences in serotonin recept?rs and MRNA, and glucocorticoid receptors in monkeys with low or high CSF 5-HIAA concentrations. (4) PET studies continued to investigate corticotrophin releasing hormone differences in subjects with low and high CSF 5-HIAA concentrations. SPECT studies continued to investigate the role of differential serotonin receptors in subjects with low and high CSF 5-HIAA concentrations.